kempkes reduction of energy use by efficicent cooling of
TRANSCRIPT
9/8/2010
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Reduction of energy use by efficient cooling of
strawberries:from model calculation to implementation in a commercial greenhouse
Frank Kempkes, Wageningen UR Greenhouse HorticultureIn cooperation with:Ruud Maaswinkel & Wouter Verkerke: Wageningen UR Greenhouse HorticultureAd van Laarhoven & Marcel Beekers: DLV PlantPeter Geelen: Peter Geelen Horticulture growing analysis and trainingMarcel Dings: Dings aardbeien bv.
Problem of strawberry cultivation: history� Start of crop cycle begin of August
� Enough assimilates (light) for
� Production and flower bud development
But:
� A premature harvest with low production
� Growers postpone start to second half of august.
� Extra energy cost
How to create a cooler night climate?
A grower had already installed coolers in his greenhouse
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Was quite poor:
� It was difficult to reduce greenhouse air temperature during night
How to improve?
� Expert panel with goal:
� Create hypothesis growing strawberries
� How to use and improve efficiency of cooling
� No restrictions to crop production and quality
� Reduction of energy consumption from 20 m3/m2 to 14 m3/m2
Result of cooling
Strawberry expert panel (1)
Series of discussions with a group of experts: strawberry, technicians etc.
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Strawberry expert panel (2)
Result of discussion:
Hypothesis: Start in begin of August
� Produces enough assimilates for production and an early start of bud development
� Cooling (reducing night temperature Aug<Sept) will spread production and increase fruit weight
� Synchronize harvest and flower bud development for spring crop cycle results in energy saving
� Create light< and temperature sum nearby “ideal”
According: 13.4 + 0.2 oC per 100 J/cm2
Strawberry expert panel (3)
How to reduce energy use?
� Mechanical cooling will increase energy use
� Other cooling methods misting, shading
� In practice severe use of minimum pipe temperatures for humidity control � air movement around the plant
� Misting as cooling method during night?
� Too high humidity
� At high humidity cooling stops
� Natural ventilation (temperature effect) will decrease
� With model calculation optimize the experimental setup
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Model calculations (1)
Course of low cooling result:
heat capacity of the greenhouse (soil)
� Model calculations showed an increase of cooling result when floor was insulated
� Optimization for costs (is insulation rate)
� Permanent? � movable or non movable
� Different effect on greenhouse climate (year around)
Model calculations (2)
Which insulation solutions are feasible? � Sustainable
� Easy to use
� Withstand greenhouse environment
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Model calculations (3)
For climate and energy use movable insulation is best option � solution
Inflatable mattress of aluminized foil
When inflated insulation of warm floor
Cold air flows to fruits
Model calculations (4)
4 8 12 16 2010
15
20
25
30
35[oC]
ref TSoil
ref TFlr
iso TSoil
iso TFlr
Effect insulation
Higher daytime & lower nighttime
� Finally: permanent EPS (extruded polystyrene) plates 40 mm thick
� Energy balance of greenhouse changes
� Effect on soil and floor temperature � air temperature
� Average floor and soil temperature for reference and isolated floor from August 10 – September 10th
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Setup of experiment (3 treatments)
Vertical fans
one per 220 m2
Sect. 2
Night misting with side-wall vents
Sect.1
Reference
Sect .4
Mechanical cooling without floor insulation
Sect. 3
Mechanical cooling with floor insulation
Concrete walk way
Vertical screens for segmentation
Location of side wall fans
Sect. 2
Night misting with side-wall vents
Sect.1
Reference
Sect .4
Mechanical cooling without floor insulation
Sect. 3
Mechanical cooling with floor insulation
Concrete walk way
Vertical screens for segmentation
Location of side wall fansMisting
300 ml/m2/h
Investments
� Local differences
� Shown numbers are a direction for Dutch situation
� Misting 6 € /m2
� Vertical fans 3 € /m2
� Mechanical cooling 20 € /m2
� Side wall fans 2 € /m2
� Insulation 1 € /cm/m2 (4 cm)
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Setup of experiment
Side wall fans capacity 8000 m3/h each
� inside 15 oC, 90%
� outside 20 oC, 50%
Cool capacity rather poor � 30 W/m2
� One unit per 200 m2
� Coolers max capacity 200 W/m2
� With & without distribution ducts
Experiment
Plants (CV Elsanta) were planted August 10 and 11th
Crop cycle divided in three periods:
� August 10 < January 5th and 10th
� 3 – 4 weeks cold
� January 28th – June 13th
� Autumn
� first harvest September 22nd – 28th
� Last harvest December 15th – 22nd
� Spring
� Harvest April 5th – June 13th
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Use of systems: Autumn
misting
Section Cum. Puls time day
[h]
Cum. Puls time night
[h]
coolers
[h]
Side wall fans [h]
1 134 2 134 11 257
3 141 180 4 141 180
� Only 4 % of run time of side wall fans misting could operate� cooling capacity limited
� Extensive use of misting during day time (Aug. – mid. Oct.)
� Coolers only 25 days used
Use of systems: Spring
� Side wall fans & misting not used
� Mechanical coolers not used
� Extensive use of misting during day time (April – June)
� Difference in misting is mainly a side effect of floor insulation
11<01 02<02 24<02 18<03 09<04 01<05 23<05 14<060
50
100
150
200
[date]
[hours]
section 1 & 2
section 3 & 4
No effect expected on climate by experiment except floor insulation}
Cumulated pulse time of misting system in spring
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Experiment: effect of cooling on temperature
16 20 24 4 810
15
20
25
30
35
[hours]
[oC]
sect . 1
sect . 2
sect . 3
sect . 4
out side
Start cooling Stop cooling
� During daytime about 3 oC below outside air temperature
� In night sections 2, 3 and 4 are in average 1.2, 6.7 and 3.7oC lower then section 1 (reference).
August 24th 12:00 till 25th 12:00
Experiment: effect on air temperature
4 8 12 16 2010
15
20
[hours]
[oC]
sect . 1
sect . 2
sect . 3
sect . 4
� Insulation decrease night temperature by 1.5 oC
� Daytime effect in section 3 is result of experimental set<up
� Section 3 more humid (RH)
Average twenty<four hours temperature course August – December
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Experiment: effect on air temperature
33 38 43 48 5310
12
14
16
18
20
daytemp. [oC]
weeknumber
sect. 1
sect. 2
sect. 3
sect. 4
ideal
� Week 33 – 40 section 3 about as ideal
� Week 40 – 53 section 1 about ideal rest to cold
Average week temperature
Experiment: effect on humidity
4 8 12 16 2075
80
85
90
95
[hours]
RH [%]
sect. 1
sect. 2
sect. 3
sect. 4
� During night because of low temperatures higher humidity
Average RH during day between August 11th and January 5th
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Experiment: energy use autumn
11<8 1<9 22<9 13<10 3<11 24<11 15<12 05<010
50
100
150
200
250
[MJ/m
2]
sect. 1
sect. 2
sect. 3
sect. 4
� Differences between section 1 & 4 and 2 & 3 are small
� Continuation of heating in section 3 and 4 for 6 days cost about 25 MJ/m2
Cumulated energy use in autumn
1m3 natural gas is 31.65 MJ
Experiment: effect on climate & energy
section Degrees hours [oC] Energy use [MJ/m2]
cooling heating 08/10 –
09/11 Autumn Spring Autmn Spring total Autumn Spring total
1 11534 38381 36138 184 210 394 2 11342 37433 34238 218 220 438 3 10224 35328 34332 34 – 34 240 220 460 4 11082 37185 35581 43 – 43 197 216 413
� Autumn section 3 lowest in degrees hours
� Spring section 2 and 3 lowest but differences smaller
� In spring as expected small differences in energy use
� Overall energy use section 3 highest
� Difference in cooling energy is air temperature difference
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Results: Crop
section Production [kg/m2]
Aut-
umn spring total
1 5.2 9.3 14.5 2 5.4 9.6 15.0 3 5.4 9.2 14.6 4 5.4 9.6 14.9
� Over whole crop cycle (Aug – May) no significant differences in
� Crop growth
� Yield
� Quality
� Average fruit weight.
Results: Crop
� During active cooling in cooled sections
� Plant load lower
� Average fruit weight higher
� Production of fruits lower
� Cooling was realized according to plan but we did not not succeeded to spread the harvest.
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Conclusions (1)
� Mechanical cooling in combination with floor insulation can reduce night temperature.
� Mechanical cooling increases energy use
� Where is the cold water produced? � not taken into account in shown numbers
� Planting date in sections with mechanical cooling was about a week to late.
Conclusions (2)
� Misting has more effect on climate then mechanical cooling.
� Reduces even at day time greenhouse air temperature
� It will increase humidity (prevents extreme low humidity with young plants)
� Use of cooling systems was limited (in time)
� Expensive investment
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Conclusions (3)
� Energy use by early start in august in combination with use of vertical fans drops from around 20 m3/m2
(common practice) to about 14 (season 2009<2010)
� Main energy saving is result of reduction of use of minimum pipe
� On time start 2 < 2 .5 m3/m2
� Small increase of energy use by floor insulation
Questions?